Hi,
I am trying to understand the process of launching a service at system
init and during runtime. I read through the various posts and the
following is what I understood so far:
During system init:
- At system init, we read the init.rc file and add a bunch of services
with a particular userId. E.g., The following lines:
service media /system/bin/mediaserver
user media
It indicates to launch a program "mediaserver" with the userid
"media".
- This "mediaserver" [defined in frameworks/base/media/
mediaserver/...] essentially adds a few services to the services list
"svclist" [defined in frameworks/base/cmds/servicemanager/
service_manager.c].
- During the process of "add_service", there is a check
(svc_can_register) to make sure that the userid with which the service
is being added is in the approved list as defined in the array of
allowed services (allowed[] ).
With the above information, I was able to launch my own test server
and then write a console app. to access it.
Using AIDL:
- I was able to implement a service and the inherent IPC mechanism
using the steps detailed in http://code.google.com/android/reference/aidl.html.
- I even looked at the corresponding .java file that gets generated as
part of the build process.
addService from Java:
Next, I tried to read how services are added from Java.
- I looked at frameworks/base/services/java/com/android/server/
SystemServer.java.
- This translates to a call in frameworks/base/core/java/andrid/os/
ServiceManager.java and then to frameworks/base/core/java/andrid/os/
ServiceManagerNative.java.
- Here, there is a remote call to call native "addService" in
frameworks/base/cmds/runtime/ServiceManager.cpp.
- The requested service is added to a KeyedVector "mServices".
Service as an application component:
http://code.google.com/android/reference/android/app/Service.html
If any of the above is incorrect, please twist my arm now.
Now, I am trying to see how I can launch a native service during
runtime that has the following characteristics: (I am lost looking at
the code and need some fresh ideas)
- It needs access to a private directory that no other service can
access -- For this, I was thinking of launching the service from a
Java .apk file (through a JNI) because each application would have
it's own private directory.
- It needs to be accessible to other services, say mediaservice.
- It needs a way to validate the calls, i.e., it should honor calls
only from a trusted service.
I hope this thread can capture enough information for future
reference.
Thanks,
Ravi
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